It is possible this name is derived from Slavic "žrŭnovy", meaning (village or valley) "of the mill". In the 14th century, German documents used the name Rasnov, but the modern German name, Rosenau, is based on a popular etymology, being influenced by the German word "Rose".

In Râșnov a citadel was built around the year 1215 by the Teutonic Knights and it was mentioned for the first time in 1331. The citadel was conquered only once in its history, around the year 1600 by Gabriel Báthory.

There is a myth attached to Râșnov Citadel. During a particularly long siege of the fortress, the citizens of Râşnov were concerned about the lack of available fresh drinking water. Two Turkish soldiers, having been captured earlier, were put to the task of digging a well in the centre of the fortress. These two men were assured that they would be given their freedom once the well was completed. According to local legend, it took them 17 years to finish the well, but they were still killed afterwards. This famous well still sits in the centre of Râșnov Fortress, and is 143 metres deep.